"With an ambition to be diesel free by 2020, 12.5 per cent of these towers need to be retrofitted (with renewable energy source) every year...telecom companies average savings would be Rs 10,000 crore every year that adds up to nearly Rs 80,000 crore over the 8 year period," the report said.

It added the government will be able to save subsidies of around Rs 273 crore every year from reduction in use of diesel.

The report said India has 4,00,000 network towers and over 70 per cent of them are located in off-grid (not connected to electricity supplied through grid), rural and semi-urban locations.

It estimates that 60 per cent of these towers are placed in indoor shelters as the old generation equipment cannot function beyond certain temperatures.

"Currently rural outdoor tower sites' biggest expense is caused by per unit (kWh) electricity from diesel...In such areas, the unit cost of electricity can go up to as high as Rs 80-90/kWh," the report said.

The NGO's report said that as first step, telecom companies should eliminate diesel consumption in rural and semi-urban areas that account for 70 per cent of total towers.

"This constitutes a total of 280,000 towers, out of which around 20 per cent are in areas where the average electricity availability is less than 4 hours," the report said.

It added that companies should gradually eliminate diesel from towers in urban regions.

"This would eliminate an average of 390 million litres of diesel usage every year and an estimated amount of about 3 to 3.2 billion litres by 2020...it would also prevent a carbon emission on an average of 1 million tons every year into the atmosphere," the report said.

The NGO report said that the deployment of new and energy efficient equipment would bring the demand close to 640 megawatt of solar equivalent renewable energy power to fill the electricity gap after the elimination of diesel.

Based on assumption that an average rural and semi-urban tower has to be powered by renewable energy for 8-10 hours, the report said that this would require an average of 760 MW of solar equivalent renewable energy capacity.

"It calls for an investment of Rs 8,360 crore per year with the total required investment close to Rs 67,000 crore by 2020. In comparison the operational expenses based on diesel would be around Rs 80,000 crore," it said.

Greenpeace India campaigner Mrinmoy Chattaraj said that telecom operators need to build trust and cooperation among stakeholders to bolster investor confidence and to overcome the problem of high interest rates in India. "The money is on the table, it's just on the wrong plates," Chattaraj said.